The present invention relates to a thrust ball bearing to be interposed between two members which make an eccentric rotary movement therebetween as in the case of a revolving scroll member and a stationary scroll member in a scroll compressor.
For example, a scroll compressor, as shown in FIG. 5, comprises a revolving scroll member 11 and a stationary scroll member 12 which are respectively provided with screw-like partition walls 11b and 12b, the arrangement being such that a compression chamber P defined between the screw-like partition walls 11b, 12b is caused to change in volume as the eccentric rotary movement of the revolving scroll member 11 (scroll rotation) relative to the stationary scroll member 12 proceeds, thereby compressing the fluid in the compression chamber P.
The axis of the revolving scroll member 11 and the axis of a driving motor 15 are shifted from each other by an amount of eccentricity e, so that when an output shaft 15a of the driving motor 15 is rotated, the revolving scroll member 11 makes an eccentric rotation with a revolving radius which is equal to the eccentricity e. At this time, the revolving scroll member 11 is acted on by a force which causes it to rotate around its own axis, while it is also subjected to a thrust load which attends the compression of the fluid. Thus, in order to prevent the revolving scroll member 11 from rotating around its own axis and to support the thrust load, a thrust ball bearing 14 is interposed between the revolving scroll member 11 and the stationary scroll member 12 (in the illustrated arrangement, a stationary frame 13 fixed to the stationary scroll member 12).
The thrust ball bearing 14 is comprised of a pair of bearing rings 14a, 14b of the same shape, and a plurality of balls 14c interposed between these bearing rings 14a, 14b. The bearing rings 14a, 14b are fixed to respective axially opposed mounts 11a and 13a of the revolving scroll members 11 and the stationary frame 13.
As shown in FIG. 6, one end surface of the bearing ring 14a (14b) is formed with a plurality of raceway surfaces 14a1 (14b1) on the same circumference. Each raceway surface 14a1 (14b1) is annular and, with eccentric rotation of the revolving scroll member 11, the balls 14c roll on the pitch circles PCD of the raceway surfaces 14a1 (14b1). The diameter d of the pitch circle PCD of each raceway surface 14a1 (14b1) is equal to the eccentricity e.
The bearing ring 14a (14b) of the shape described above is produced, for example, from a steel sheet blank through a series of processing steps: press work.fwdarw.heat treatment (for example, carburizing).fwdarw.finishing of the raceway surfaces 14a1 (14b1).
Generally, it is known that when a rolling bearing is rolling under a load, repetitive stress on the rolling contact surface produce cracks in the material, leading to flaking (separation into flakes due to fatigue), causing the expiration of the rolling contact life.
It is therefore an object of the invention to suppress the flaking of the raceway surfaces (rolling contact surfaces) of a thrust ball bearing of the type described above so as to increase the rolling contact life.